Thin film magnetic recording discs and disc drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method involves a floating transducer head gliding at a predetermined distance from the surface of the disc due to dynamic pressure effects caused by air flow generated between the sliding surfaces of the transducer head and the disc. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disc rotates, such that the transducer head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the surface of the disc at a desired position in a data zone.
In conventional hard disc drives, data are stored in terms of bits along tracks. In operation, the disc is rotated at relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which positions the head radially on the disc surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disc, i.e. over a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially on the disc surface between tracks. Many actuator arms are rotary, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm. A linear actuator may alternatively be used to move a magnetic head assembly inward or outward on the disc along a straight line.
To record information on the disc, the transducer creates a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium (known as “saturating” the medium), and grains of the recording medium at that location are magnetized with a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the saturating magnetic field is removed. As the disc rotates, the direction of the writing magnetic field is alternated based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, typically eight bits form a byte and bytes of data are grouped as sectors. Reading or writing a sector requires knowing the physical location of the data in the data zone so that the servo-controller of the disc drive can accurately position the read/write heads in the correct location at the correct time. Most disc drives use embedded “servo patterns” of recorded information on the disc. The servo patterns are read by the magnetic head assembly to inform the disc drive of track location. In conventional disc drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a “servo burst”. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is a time consuming process.
Servo patterns are conventionally formed by a read-write head and opto-mechanical positioning device. An alternative approach to the servo-sensing problem comprises the use of mechanical voids or depressions in the magnetic layer between tracks formed by stamping or otherwise physically marking a pattern on the disc to function as servo patterns. A magnetic material layer is then applied at a consistent thickness over the entire disc surface. When this type of disc is used, the distance from the magnetic head to magnetic material in the depressions is further than the distance from the magnetic head to magnetic material in the track. The increased distance both reduces the strength of the signal recorded in the depressions and reduces the contribution from the depressions to the magnetic field sensed by the read head.
While the depressions or voids formed in the disc are helpful in increasing track density, they tend to reduce the tribological performance of the disc assembly. For example, during operation of the magnetic recording medium, the slider no longer travels over a smooth surface and thus causes several mechanical performance drawbacks. These drawbacks include modulation of fly height when encountering servo patterns, fly height perturbations due to topography changes from the track width definition, glide defects from the stamping process, and disc distortion due to the servo patterning process. It is preferred therefore to provide the servo pattern without surface topography.
Several approaches to forming servo-patterns are disclosed in the prior art. For example, U.S. Pat. No. 6,153,281 and U.S. Pat. No. 5,858,474, both to Meyer et al., disclose a magnetic medium having permanently defined boundaries between tracks and a consistent surface smoothness. Servo-patterns are formed, in part, by laser ablation, laser heating, photolithography, perpendicular deposition, ion milling, reverse sputtering, and ion implantation and can be used individually or in combination, with either the magnetic layer or underlayer, to create relatively non-magnetic areas. U.S. Pat. Nos. 6,086,961 and 5,991,104, both to Bonyhard, disclose creating non-magnetic areas in the formation of servo-sensing patterns by ion implantation where the ion implantation destroys the magnetic properties of the magnetic layer.
Still other art discloses methods for forming servo-patterns as U.S. Pat. No. 6,055,139 to Ohtsuka et al. where implanting chromium ions into a hard magnetic disc is used to change regions of the magnetic layer into non-magnetic regions. U.S. Pat. No. 4,556,597 to Best et al. discloses a magnetic recording disc substrate provided with a capacitive servo-pattern formed by implanting doped materials in the substrate to modify the substrate conductivity. Sargunar, in U.K. 1,443,248, discloses magnetic recording medium and methods for making the medium by forming low coercivity regions in the medium by implanting chromium ions. However, it is believed that the use of such metal ions adversely damages the magnetic layer.
Although the art has recognized forming servo-patterns and marks on magnetic medium without substantially altering the topography of the media, an additional need exists for increasing areal density, smoothness and throughput of magnetic recording media.
Thus, there exists a continuing need for magnetic recording media having servo-marks which occupy a reduced area of the media surface thereby increasing, available area for recording data. There also exists a need for an efficient, economical fabrication methodology enabling the recording of servo information on a magnetic medium without adversely affecting topography.